The organic EL display device can perform high luminance display due to spontaneous light emission and is suitable for a small area display. Therefore, the organic EL display device has been paid attention as a next generation display device to be mounted on a portable telephone set, a PHS, a DVD player or a PDA (digital portable terminal device).
In a portable telephone set, for example, a main display panel and a sub-display panel are arranged back to back. A switching of display is performed between the sub-display panel provided on a front side of a cover of the organic EL display device to display information necessary for the sub-display panel when the cover is closed and to display operation information such as a menu on the main display panel provided on a rear side of the cover when the cover is opened.
In this case, the main display panel is for a high resolution color display and the sub-display panel having display area smaller than that of the main display is for a monochromatic display. In particular, the sub-display panel of the portable telephone set displays time and image of a call when a signal is received.
Drivers of the main display panel and the sub-display panel have different specifications and are chipped on respective display substrates. Therefore, these drivers are usually provided separately.
A current drive circuit of the organic EL display panel includes current source drive circuits, for example, output circuits formed by current mirror circuits corresponding to respective terminal pins (column pins), regardless of the type of the organic EL panel, active matrix type or passive matrix type.
In the active matrix type organic EL panel, pixel circuits are provided correspondingly to display cells (pixels) and each pixel circuit drives a transistor according to a voltage stored in a capacitor and the organic EL element (referred to as “OEL element”, hereinafter) is current-driven by the transistor.
On the other hand, in the passive matrix type organic EL panel, anodes of the OEL elements arranged in a matrix are connected to output pins of drive current sources through column pins and the OEL elements are driven by the respective drive circuits.
Incidentally, a drive circuit for an organic EL display panel, which is constructed with D/A converter circuits provided correspondingly to column pins, is disclosed in JP2003-234655A (Patent Reference 1). In the drive circuit disclosed in Patent Reference 1, the D/A converter circuits provided correspondingly to the column pins receive display data and a reference drive current, converts the digital display data into an analog signal according to the reference drive current and generates drive currents corresponding to the respective column pins or a current on which the drive currents are generated.
Patent Reference 1: JP2003-234655A